Just the thought of coming face-to-face with a real, live mountain lion is enough to raise the pulse and blood pressure of most people, and in fact, more people have been spotting them on the eastern slopes of Sonoma Mountain.

The animals have popped up in such unlikely places as downtown Sebastopol last Thursday and downtown Berkeley this spring, and few people haven't heard of at least some neighbor or friend of a friend who's had an encounter with California's top predator, next to humans.

The number of mountain lions (puma concolor) roaming Sonoma Mountain has been steadily increasing since hunting them was banned by public referendum in 1990, but loss of habitat and the ability to get from one preserve to another are causing problems for people who live near wild lands and the big cats.

More than 12,000 were killed while California offered a bounty on them from 1907 to 1963 — more than any other state — until then-governor Ronald Reagan signed a hunting moratorium. Voters made the ban permanent in 1990 with Proposition 117, passed by a 52 percent majority.

Solitary by nature and reclusive by habit, mountain lions are the apex predator wherever they live (aside from humans), subsisting on deer, moose, elk, mountain goats and smaller mammals such as rabbits, raccoons, skunk and even mice when they're handy. They will also take livestock and pets on occasion. Human deaths from mountain lion attacks are extremely rare.

Linda High, a long-time sheep rancher at the 2,000-foot elevation of Sonoma Mountain, has lost up to five sheep at a time, in recurring incidents over the past several years. She has seen big cats in the road and driveways on several occasions.

While she admires wild animals and detests trapping and killing them, the continuing predation left High no choice but to call in a trapper from California Department of Fish &amp; Game, who eventually trapped and killed a male, female and two cubs.

Multiple kill sessions are not typical for mountain lions. "A young male will come in and slaughter five or six animals in one night," High said. "You have carnage between the house and barn, even near a fenced area. The barn doesn't protect them in any way."

Another neighbor, who preferred not to be identified, said, "I don't think the lions are good or bad, but things are happening at a frustrating level as to how we protect our animals. I have these animals and it's my job to protect them. I feel helpless when I come home and find them dead."

Zara McDonald, a conservationist and expert on mountain lions, said that multiple kills are rare, but they do happen.

"There are rare incidences where a lion may get into an enclosure with goats or sheep and a killer instinct sets in where it becomes play for them," McDonald said. "It's not about food anymore. This is a natural cat behavior, similar to a house cat."

"This is the reason that all residents should bring pets and pet food in at night, hobby animal owners and ranchers should take the responsibility to properly enclose and/or protect their animals," she said. "The pumas are moving as they do naturally, trying to survive on an increasingly fragmented landscape. They are opportunists."

McDonald is executive director of Felidae Conservation Fund as well as the Bay Area Puma Project.

Mountain lion sport hunting is prohibited, but depredation licenses are issued when they kill livestock and after any incident where a mountain lion is considered to be a threat to public safety.

"These cats are very fearless of people," High said. "I feel bad about shooting them, but there are so many and there is so much (livestock) killed, it's really hard not to. We try not to let the kids out the door."

Another neighbor, Mary McChesney, isn't as worried about them.

"I don't see that they are a bother," she said, having watched a mountain lion stroll up her driveway and up to her art studio on the property she has lived for almost 50 years. "It's in their territory and they are not frightened. I'm amazed at their self-confidence, coming out in daylight."

While mountain lions have killed people, fatal attacks are extremely rare, with fewer than a dozen reported in California since 1893, most involving children or small-sized adults.

Unfortunately, there is little concrete data about these creatures, mostly because they are so solitary and so seldom interact with people. There are thousands of reported sightings, but very few of those can be confirmed. Identifying the cats is made more difficult because they are most active in twilight hours.

The latest published figures from the California Department of Fish &amp; Game include up to 2007, and show almost 400 reported incidents, including sightings, with only 21 of those involving any danger to people. Five cougars were killed in 2007 as a result, statewide. California did not participate in the latest Mountain Lion Conference held in Montana this May and has published no recent information about them.

A rule of thumb is that the cat population rises with the prey population, said Kyle Orr, the public information officer for the state Fish &amp; Game. He said that the overall population, statewide, is not increasing significantly, noting that depredation licenses to kill cougars in Sonoma County have been fairly uniform from 2005 to 2009.

In Northern California, McDonald has set out to learn more about these animals through the Bay Area Puma Project, starting with an extensive study in the Santa Cruz mountains, that has been placing electronic collars on captured cats since 2008 that enables detailed tracking. See www.bapp.org for more information.

She observed that female pumas have home ranges from 23 to 50 square miles, but that males can range up to 300 square miles. There are no numbers for the Sonoma County population, but she expects to be tracking them north of the Golden Gate Bridge in the next two years.

"Humans are not on their menu, or many of us would be dying every day," she said. "They avoid humans and our towns, but it has become increasingly difficult because of encroachment." She said there are only six known deaths in California since 1890 and zero verified attacks in the Bay Area since 1909.

Mountain lions once roamed freely throughout North and South America. They were practically decimated east of the Mississippi by 1900, but have managed to hang on fairly well in the western parts of the country. They breed year round, but typically half of the cubs die in the first year. They are not an endangered species, but their habitats are threatened everywhere.

"We play a big role in their existence," McDonald said. "We ultimately determine the outcome. We can chose to have these important, top-down regulators in our ecosystems or we can extirpate them as the eastern half of this country did by 1900.

"If we lose them, we will see an explosion of deer, and on top of that, sick and diseased deer, and increase in Lyme disease and other diseases, and serious losses of critical habitat for a spectrum of other species. Lastly, every deer kill that a puma makes is fed on and supports an array of other species. What would our natural world become without the puma in it? Biodiversity will not longer be a word associated with Northern California."

As the availability of open spaces steadily declines, and the corridors between those spaces close off, the big cats are increasingly penetrating human habitations, according to all sources questioned. More study is needed to see if the population must be managed more aggressively in the future, better methods for preserving their ranges can be found, or both.